Mooderator2.

NULL

Staff Member

That should work, but why does the OAK have to penetrate the slab? I would prefer it to go out the wall in back of the stove.

PE Alderlea T6 - the gentle giant and a Jotul 602, the little stove that could“Sometimes I wonder whether the world is being run by smart people who are putting us on, or by imbeciles who really mean it.” - Mark Twain -
"A poor worker always blames his tools." - Dad

Feeling the Heat2.

NULL

Can you put in a raised hearth and run the vent pipe inside an interior wall to get to the outside? You' d probably need to go to a 2x6 interior wall, in order to get the largest pipe possible (4" ???) in the wall. That would give you the longer run you need. Burnt03 is correct about the elbows adding effective length.

Member2.

NULL

Been a long time since I calculated pipe flow resistance... but long story short is, anything moving through a pipe (air, water, solids) experiences friction. Long pipe runs and small diameter pipe can create enough resistance to flow that you won't get sufficient airflow to fire your stove. Imagine the difference between sucking water out of a straw vs. out of a 1/2" copper pipe. Small increase in diameter allows significant increase in flow at reduced restrictions.

Member2.

NULL

And some searching online shows 5" OAK's available for some stoves (drolet).

If you're doing something in a slab that you can't change later, you may want to oversize now. Too much air can't hurt, because you can throttle it back. I wouldn't run vent pipe up the wall to draw attic air... your creating another chimney with the fresh air pipe... you may have problems with the smoke backdrafting into the fresh air tube. Best to run it outside, down low.

You might want to consider running two pipes under the slab (if that's the route you go)... run two 3-4" pipes (or larger if your budget allows and the distance is long)... where you come out of the slab, use a "T' to combine to a single pipe and connect that to the fresh air to the stove. Remember that the larger you can go, the better...

Feeling the Heat2.

NULL

And any open pipe will naturally be occupied by the first "right sized" critter that finds it. Preventing that requires a screen or grill, which can be blocked by leaves or other detritus sucked or pushed up against the opening. An intake high up above the ground or structure such as a deck is much preferred, as a blocked outside air pipe will cause all kinds of grief when the stove is going.

A ground level air intake can also be blocked by storm water under the right circumstances.

All part of the reason that when decision time came, we went with no OAK. We saved money, too. We don't miss it a bit.

Also, there is a discussion of the pros and cons of OAKs on woodheat.org that comes down against them.

Minister of Fire2.

NULL

For a 16' run I would use 4" for the under slab portion and then hook up to the stove using the 3" stuff. You only get one chance to get the under slab portion right. Any pipe will work so long as it is strong enough to withstand the weight of the concrete and installers during the pour. I've done this with a 4" dryer vent in a slab using schedule 40 pvc. Some stoves, maybe a future stove, requires 4" so you want to be ready.

OAK setups are great and there is no good reason to not install one. Generally it is a lazy installer that wants to skip the OAK.

Don't go up any higher than necessary on the intake end, the OAK becomes a chimney to some extent as a previous poster wrote.